MEMS Structure And Method Of Forming Same

ABSTRACT

A microelectromechanical system (MEMS) device that reduces or eliminates stiction includes a substrate and a movable element at least partially suspended above the substrate and having at least one degree of freedom. A protrusion extends from the substrate and is configured to contact the movable element when the moving element moves in the at least one degree of freedom. The protrusion comprises a surface having a low surface energy relative a silicon oxide surface. The protrusion may be coupled to a voltage potential node to avoid or counteract electrostatic forces.

This application claims the benefit of U.S. Provisional Application Ser.No. 61/506,526, filed on Jul. 11, 2011, entitled “MEMS Structure AndMethod Of Forming Same,” which application is hereby incorporated hereinby reference.

BACKGROUND

Microelectromechanical systems (MEMS) come in a variety of forms and areused for a host of different applications. Many MEMS include a movableelement, such as a flexible membrane (e.g., in a deformable mirrordevice), a cantilevered beam (e.g., in a motion sensor), a series offingers in a comb structure (e.g., in an accelerometer), and the like.MEMS frequently suffer from the phenomenon known as stiction. Stiction,which is derived from the words static and friction, refers to theundesirable consequence of a movable element in a MEMS device contactingand becoming stuck to a surrounding feature.

The phenomenon of stiction can arise during operation of the MEMS deviceand/or during manufacture of the device. Various environmental factorsand processes that take place during the manufacture of a MEMS devicecan give rise to stiction. Wet processes, such as photoresist strips,water rinses, solvent cleans, and the like and dry processes such asplasma etch and plasma clean steps, in particular, can createcircumstances wherein friction is likely to occur. This phenomenon canimpede or even prevent the proper operation of the MEMS device.

What is needed, then, is a MEMS structure that can overcome the abovedescribed shortcomings in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 a illustrates in cross-sectional view an illustrative embodimentof a MEMS device and FIG. 1 b illustrates the same MEMS device in planview;

FIGS. 2 a and 2 b illustrate in cross-sectional view other illustrativeembodiment MEMS devices;

FIGS. 3 a through 3 c schematically illustrate forces acting upon a MEMSstructure during manufacturing steps;

FIGS. 4 a through 4 f illustrate steps in the manufacture of anillustrative embodiment MEMS device;

FIG. 5 illustrates another embodiment MEMS device;

FIG. 6 illustrates yet another embodiment MEMS device;

FIGS. 7 a through 7 e illustrate steps in the manufacture of the MEMSdevice illustrated in FIG. 6; and

FIGS. 8 and 8 a illustrate still another illustrative embodiment MEMSdevice.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A first illustrative embodiment MEMS device 1 is illustrated in FIG. 1a. MEMS device includes at least one movable element 2 at leastpartially suspended above a cavity 4 formed in a substrate 6. FIG. 1 ais a cross-sectional view of MEMS device 1. For reference, FIG. 1 billustrates a plan view of MEMS 1 wherein FIG. 1 a is taken across theline indicated by A-A′ in FIG. 1 b. As best illustrated by FIG. 1 b,MEMS device 2 comprises a series on interdigitated fingers, 2 a, 2 b, 2c, 2 d, etc., each of which is fixed at one end and is free at the otherend. The free ends of the interdigitated fingers extend over, in otherwords are cantilevered over, cavity 4 formed in substrate 6. The size,number, and placement of the interdigitated fingers 2 a, 2 b, 2 c, 2 d,etc., are for illustration and any number size and placement ofinterdigitated fingers is contemplated within the present disclosure. Aswill be addressed in more detail below, movable elements 2 may be formedby patterning a wafer 14 into the desired patterns. The MEMS device 1illustrated in FIGS. 1 a and 1 b is commonly referred to as a combstructure. In other embodiments, MEMS device 1 can take the form of asingle cantilevered beam extending over a cavity, a flexible membranesuspended over a substrate or a cavity in a substrate, or any other wellknown alternatives.

One skilled in the art will recognize that substrate 6 comprises a stackof dielectric layers 8 formed atop a wafer 12. Embedded within the stackof dielectric layers are various metal interconnect features 10.Dielectric layers 8 and metal interconnects 10 are formed using knownback-end-of-line (BEOL) techniques common to the semiconductor industryand are not repeated herein. As illustrated, three layers of metalinterconnects are embedded within three dielectric layers, althoughother numbers of layers and arrangements are also within thecontemplated scope of this disclosure.

Wafer 12 may comprises a bulk silicon wafer. In other embodiments, wafer12 may comprise any semiconductor substrate, ceramic substrate, quartzsubstrate, or the like. In some embodiments, wafer 12 comprises asilicon-on-insulator (SOI) or other composite wafer. Active and passivecomponents, such as transistors, diodes, resistors and the like (notshown) may be formed in and on substrate 12.

In the embodiment illustrated in FIG. 1 a, a top dielectric layer 9 isformed above the top dielectric layer 8 and atop the top metal layer 10,using well known processing techniques. This top dielectric layer may besilicon oxide, although other dielectrics such as silicon oxynitride,silicon nitride, and the like are also contemplated. It is in topdielectric layer 9 that cavity 4 is formed using well known patterningand etching techniques.

A second wafer 14 is then placed atop top dielectric layer 9. In oneembodiment, wafer 14 is a silicon wafer and top dielectric layer 9 is asilicon oxide layer. Fusion bonding is employed to ensure a strong bondbetween wafer silicon wafer 14 and silicon oxide top dielectric layer 9.As those skilled in the art will appreciate, wafer 14 can be thinned andpatterned to form movable elements 2. Electrical contact to MEMS device1 and/or to components formed in and on wafer 12 can be made throughcontacts 14. The resulting structure is a MEMS device 1 having a movableelement 2 that may be, but is not required to be, formed over a cavity4, to allow for free movement in at least one axis (the z axis in thecase illustrated in FIGS. 1 a and 1 b).

MEMS device 1 further includes protrusions 16 in cavity 4. Protrusions16 are designed and positioned such that a movable element 2 willcontact one or more of protrusions 16 when the movable element 2 isdeflected downward into the cavity, i.e. in the z direction. In FIG. 1a, two cavities 4 are illustrated, each having two protrusions 16. Thisis a matter of mere design choice and any number of cavities iscontemplated, as well as any number and placement of protrusions 16within the cavity, or elsewhere on MEMS device 1 where movable elements2 might come in contact with another component of the device, and becomestuck thereto.

Protrusions 16 are formed by patterning and removing portions of topdielectric layer 9. This can be accomplished by, e.g., well knownphotolithography and etching steps. In some embodiments, protrusions 16have a height sufficient to extend above any sensing electrodes whichthe movable element might otherwise contact. In one embodiment, theprotrusions 16 have a height of about 1,000 Å.

As further illustrated in FIG. 1 a, protrusions 16 are coated or coveredwith a film 18. In an illustrated embodiment, film 18 comprises TiN. Anadvantageous feature of film 18 is that TiN has a lower surface energythan does silicon oxide. A lower surface energy means less attractiveforces will exist between movable elements 2 and film 18 should contactbetween the two occur, compared to the amount of attractive forces thatwould exist between movable elements 2 and protrusions 16 if protrusions16 were not coated with film 18. In illustrative embodiments, protrusion16 has a water contact angle of higher than about 15°, and in someembodiments protrusion 16 has a water contact angle in the range ofabout 20° to about 50°. In an illustrative embodiment, film 18 has athickness ranging from just a few nanometers to tens of nanometers. As apractical matter, it is desirable to have a relatively thin film 18 (thethinner the film, the shorter the deposition time and less themanufacturing costs, for instance). It is sufficient that film 18provides good coverage of protrusions 16, including at corners, and isthick enough to withstand any mechanical abrasion or deformation thatmight arise from contact with movable elements 2. In other embodiments,film 18 could comprise AlCu, amorphous Carbon, or a stacked film such asTiN/AlCu, or other semiconductor process compatible and electricallyconductive materials.

FIG. 2 a illustrates another embodiment MEMS device 1, wherein movableelement 2 is in the form of a flexible membrane at least partiallysuspended over cavity 4. Protrusions 16 coated with film 18 are formedon a bottom surface of cavity 4 so that movable element 2 contacts film18 coated protrusions 16 in the event movable element 2 is deflecteddownward. In other embodiments. FIG. 2 b illustrates yet anotherembodiment MEMS device, wherein movable element 2 is in the form of acantilevered beam at least partially suspended over the underlyingsubstrate. As in the previously described embodiments, protrusions 16are placed and formed such that movable element 2 will contact film 18when movable element 2 is deflected downward toward the underlyingsubstrate. One skilled in the art will recognize numerous variations andalternative to these illustrated embodiments and will further recognizeother placements for film 18 coated protrusions 16 are within thecontemplated scope of the present disclosure.

Returning attention now to FIG. 1 a, an additional advantageous featureof some embodiments will be discussed. Note that film 18, in addition tocovering protrusions 16, also extends over contact 11. Because film 18is conductive, this means that protrusions 16 are electrically coupledto contact 11. An advantageous feature of this embodiment is that itallows for the potential on protrusions 16 to be controlled. In oneillustrative embodiment, protrusions 16 are coupled to a groundpotential by way of film 18, contact 11, and interconnects 10. Thisembodiment allows for charge that might build up on protrusions 16 to bebled off to ground.

FIG. 3 a schematically illustrates conditions during a manufacturingprocess of MEMS device 1, wherein the device is subjected to a dryprocess, such as a plasma clean process. The plasma process isschematically illustrated by cloud 20. As is known in the art, a plasmaprocess can cause charge to build up, particularly on conductivesurfaces. In the illustrated embodiment, charge might build up onconductive film 18 covering protrusions 16. This charge can cause anelectrostatic attraction between film 18 and movable elements 2,schematically illustrated in FIG. 3 a by arrows 22. This electrostaticattraction can cause movable elements 2 to deflect downwards towardprotrusions 16 and film 18 and become stuck thereto, both by the forcesof stiction (i.e. the surface energy of film 18 and movable elements 2causing them to bond together) as well as electrostatic attraction. Thisundesirable phenomenon can be reduced or eliminated by electricallycoupling protrusion 16 and conductive film 18 to a ground potential 24by way of contacts 11 and interconnects 10.

FIG. 3 b illustrates yet another embodiment. In this embodiment,contacts 11 do not couple protrusions 16/film 18 to ground. Rather, asillustrated protrusions 16/film 18 are electrically coupled to movableelements 2 by way of contacts 11 and interconnects 10 that electricallyconnect to contacts 14. In this way, protrusions 16/film 18 can bemaintained at a potential that is the same as the potential of movableelements 2, thus reducing or eliminating electrostatic attractionbetween them, and hence reducing or eliminating the likelihood of amovable element becoming stuck to the protrusions.

Various alternative approaches will be apparent to those skilled in theart, informed by the present disclosure. For instance, one couldintroduce a switching mechanism, whereby protrusions 16/film 18 could beswitchably coupled to ground, to the movable element, or to some otherpotential voltage. Alternatively, some protrusions could be coupled toground, whereas other protrusions are coupled to other potentials.Whereas film 18 is illustrated as a continuous film covering (and henceelectrically coupling) all protrusions within a given cavity, as amatter of design choice, film 18 could be patterned to provide differentelectrical paths for different protrusions. In yet another embodiment,film 18 could couple one or more protrusions 16 to a potential voltagesource (not shown). This potential voltage source could be configured toprovide a voltage of the opposite polarity to that voltage on movableelements 2. In this way, protrusions 16 could be configured to have anelectrostatic force that repulses movable elements 2 and hencecounter-acts any electrostatic attraction that otherwise exists or thatis induced between movable elements 2 and protrusions 16.

The illustrated embodiments also provide advantageous features duringso-called wet processes involving rinse and immersion in liquids such aswater, solvents, and the like, as schematically illustrated by referencenumber 26 in FIG. 3 c. Those skilled in the art will recognize thatliquid will occupy the spaces, e.g. between movable elements 2 andprotrusions 16, as schematically illustrated by reference number 28.Depending upon the liquid and the material from which protrusions 16 andmovable elements 2 are comprised, significant attractive forces can begenerated by the capillary action of the liquid. Again, by selecting acoating, such as film 18, having a lower surface energy, the attractiveforce between protrusions 16 and liquid 28 can be reduced, thuslessening the likelihood or severity of movable elements 2 becomingstuck. One commonly employed measure of the attraction between a liquidand a surface is the so-called contact angle, which is related tosurface energy. The larger the contact angle, the lower the surfaceenergy—and hence the lower the amount of attraction between the surfaceand the liquid. As an example, silicon oxides typically have a contactangle in the range of about 0° to about 20°. By contrast, a metal filmsuch as TiN typically has a contact angle ranging from about 20° toabout 50°. Hence, the deleterious effects of capillary action andsurface tension can be reduced through film 18.

An illustrative method for forming illustrative MEMS device 1 is nowpresented with reference to FIGS. 4 a through 4 f. FIG. 4 a illustratesan intermediate point in the manufacture of MEMS device 1. As shown,wafer 12 has had formed thereon various dielectric layers 8 in whichhave been formed interconnects 10 and contacts 11. Interconnects can beformed of copper or a copper alloy, aluminum or an aluminum alloy, dopedpolysilicon, and or other conductive materials. In one embodiment, afirst layer of conductor comprises doped polysilicon and subsequentlayers of conductor comprise copper formed using well-known damascenetechniques. Dielectric layers may comprise silicon oxide, siliconnitride, various silicon glasses, high k dielectrics, and the like, asare well known in the art. Those skilled in the art will recognize thatvarious etch stop layers, barrier layers, and the like (not shown) willlikely be employed in forming the interconnects 10. Although threedielectric layers and interconnect layers are shown, this is forillustration only and is not intended to limit the scope of thisdisclosure.

As illustrated in FIG. 4 b, a top dielectric layer 9 is formed atop theintermediate workpiece. Top dielectric layer may comprise a materialsimilar to one of dielectric layers 9 or may alternatively comprise oneor more passivation layers. In one contemplated embodiment, dielectriclayer 9 comprises silicon oxide to provide for good bonding adhesion toMEMS wafer 14 as will be described in detail below.

FIG. 4 c illustrates the intermediate workpiece after top dielectriclayer 9 has been patterned to form cavities 4 and also protrusions 16.One skilled in the art will recognize various patterning techniquescould be employed to form cavities 4 and protrusions 16. In oneembodiment, a first patterned photomask is used to protect the rest oftop dielectric layer 9 while other portions of top dielectric layer 9are removed to form protrusions 16. A second patterned photomask is thenused to protect protrusions 16 while other portions of top dielectriclayer are removed to form cavities 4. Alternatively, cavities 4 andprotrusions 16 could be formed simultaneously by blanket etching awayportions of top dielectric layer 9, followed by additional etching awayof selected portions of top dielectric layer 9 to obtain the desiredpattern. In yet other embodiments, top dielectric layer is firstselectively etched using one or more patterned photomasks, followed by ablanket (e.g. timed or end point detection) etch to complete thepattering process. Regardless of the manufacturing steps employed, theresult is a top dielectric layer 9 having cavities 4 formed therein andfurther having one or more protrusions 16 formed within one or more ofcavities 4. Although protrusions 16 are illustrated as being formed onlyon the bottom of cavities 4, it is within the contemplated scope of thepresent disclosure that protrusions could be formed on sidewalls ofcavities 4 and or on a top surface of top dielectric layer 9.

As illustrated in FIG. 4 d, film 18 is next formed over the workpiece,including over protrusions 16. Film 18 may be TiN, or some otherappropriate material and may be deposited using CVD (PECVD, etc.), PVD(sputter, evaporation, etc.), ALD, or the like, and/or a combinationthereof to a thickness of perhaps 5 to 10 nanometers.

Film 18 is next patterned using photolithography and etching techniquesto remove film 18 from much of the workpiece, but leaving film 18coating protrusions 16. In the illustrated embodiments, film 18 alsoextends over to and covers contacts 11, thus electrically coupling oneor more protrusions 16 to one or more contacts 11. As addressed above,in this way protrusions 16 can be electrically coupled to a desiredvoltage potential. In other embodiments, film 18 can be deposited orotherwise formed over protrusions 16.

Manufacture of the MEMS device continues with the process illustrated inFIG. 4 f. A MEMS wafer 14 is placed atop patterned top dielectric layer9. As addressed above, top dielectric layer 9 and wafer 14 may beselected such that the two materials form a strong bond when placed incontact. Pressure and or heat may be applied to improve or expedite thebonding process. Either before or after MEMS wafer 14 is bonded to topdielectric layer 9, MEMS wafer 14 is processed, e.g., thinned andpatterned, to form movable elements 2. Various components and electricalconnections may be formed in and on wafer 14. For instance, if wafer 14is a semiconductor material, such as silicon, various transistors andother devices (not shown) can be formed in and on wafer 14. Likewise,various interconnects can be formed in and on wafer 14. As but oneexample, FIG. 4 f illustrates vias 30 that are formed extending throughwafer 14. In the illustrated embodiments, these vias 30 are aligned withinterconnects 10. This allows for electrical coupling of movableelements 2 and or other components on wafer 14 to components on wafer12. Note that, due to the size of its cross sectional area, each via 30is illustrated as having a central void region. This is for illustrationonly, and vias 30 that are completely filled with a conductor are withinthe contemplated scope of the present disclosure. In some embodiments,via 30 comprises a through silicon via (TSV).

FIG. 5 illustrates an alternate embodiment. In this embodiment,protrusions 16 are formed directly overlying contacts 11. Film 18 isformed directly overlying protrusions 16 and contacts 11. Thisembodiment can be obtained using the processes described above withrespect to FIGS. 4 a through 4 f, albeit with a different photomaskpattern to align protrusions 16 with previously formed contacts 11.

FIG. 6 illustrates yet another embodiment MEMS structure 1. Detailsregarding this embodiment that are similar to those for the previouslydescribed embodiments will not be repeated herein. In this embodiment,protrusions 17 are formed from metal interconnect materials, similar tothe materials used in the formation of interconnects 10 and contacts 11.In some embodiments, protrusions 17 may be formed of a copper alloy. Inother embodiments, protrusions 17 may be formed of a copper alloy whichis further coated with TiN or another material selected to havedesirable properties, such as a low surface energy value. Because thesurface are of protrusions 17 is lower than the surface area of thefloor of cavity 4 and further because protrusions 17 have a lowersurface energy than does the silicon oxide material of the floor ofcavity 4, protrusions 17 have less attraction to movable elements 2 andare less likely to stick when placed in contact with movable elements 2.

FIGS. 7 a through 7 e illustrate an illustrative method for forming theMEMS device illustrated in FIG. 6. Starting with FIG. 7 a, anintermediate step in the manufacturing process is illustrated in whichvarious interconnects 10 have been formed in stacked dielectric layers 8atop substrate 12, as has been previously described. In the illustratedprocess step, a stack of metal layer 32 and metal layer 33 has beenblanket formed (e.g., deposited) over the workpiece. Layer 32 is themetal layer from which contacts 11 will subsequently be formed, asdescribed below. In some embodiments, layer 32 is copper that is blanketdeposited over the workpiece including within trenches (not shown)formed within the topmost of the stacked dielectric layers, in what iscommonly referred to as a damascene process. Layer 33 is the layer fromwhich protrusions 17 will be formed as also described below. In someembodiments, layer 33 is TiN, although other materials are alsocontemplated, as discussed above.

Next, as illustrated by FIG. 7 b, layer 33 is patterned using knownphotolithography and etching techniques to form protrusions 17. Layer 32is then patterned using similar techniques to form contacts 11 asillustrated by FIG. 7 c.

Processing then continues, as shown in FIG. 7 d, with the formation andpatterning of top dielectric layer 9 to form cavities 4. Note that thepatterning of top dielectric layer 9 is simpler in this embodiment, asit is not necessary to use extra masking steps to form protrusions16—although extra steps may be required during the formation andpatterning of metal layer 33 to form protrusions 17.

Continuing with FIG. 7 e, a MEMS wafer 14 is bonded or otherwiseattached to the workpiece, which wafer 14 is patterned and thinned toform, e.g., movable elements 2. In the illustrated embodiment, movableelement 2 is in the form of a comb structure at least partiallysuspended over cavity 4. Other movable elements such as those disclosedabove could also be employed in this embodiment Likewise, the number andplacement of protrusions 17 are for illustration only. Other numbers andplacements of protrusions 17 are within the contemplated scope of thepresent disclosure.

FIG. 8 illustrates an embodiment MEMS device 1 wherein protrusions 19are formed from metal layer 32, from which contacts 11 are also formed.In this illustrated embodiment, a single structure 19 performs thefunctions of both providing a protrusion having a low surface energy andalso connecting the protrusion to other circuitry and voltage potentialsvia interconnects 10. Also shown in FIG. 8 is a sense electrode 34located beneath movable element 2. Such sense electrodes are frequentlyemployed with MEMS devices and, although not shown, any one of the abovedescribed embodiments might also include a sense electrode locatedadjacent movable element 2. It should be noted that generally it isdesirable that movable element 2 not contact sense electrode 34—eitherduring operation or during manufacture. In some embodiments, protrusions16 or 17 or 19 are specifically arranged such that movable element 2will contact protrusions 16 or 17 or 19 prior to (and hence be preventedfrom) contacting sense electrode 34. To this end, protrusion 16 or 17 or19 may be positioned such that it is within the arc of movement ofmovable element 2 prior to sense electrode 34. This arrangement isillustrated, for instance, in FIGS. 8 and 8 a (a plan view of the areaof interest of FIG. 8). As shown, when protrusion 16 is of a same heightas sense electrode 34, advantageous features can still be obtained bypositioning protrusion 16 such that movable element will contactprotrusion 19 prior to making contact with sense electrode 34. Oneskilled in the art will recognize that protrusion 19 could be madehigher than sense electrode 34 in other embodiments.

Generally speaking embodiments include microelectromechanical system(MEMS) device having a substrate and a movable element at leastpartially suspended above the substrate and having at least one degreeof freedom. A protrusion extends from the substrate and is configured tocontact the movable element when the movable element moves in the atleast one degree of freedom. The protrusion comprises a surface having alow surface energy relative a silicon oxide surface.

Other embodiments provide for a MEMS device having a first substratewith a plurality of interconnect layers embedded in a respectiveplurality of stacked dielectric layers. A second substrate is mountedatop the first substrate and bonded to a topmost one of the dielectriclayers. The second substrate comprises a movable element at leastpartially suspended above the first substrate. A protrusion extends fromthe first substrate and is configured so as to engage the movableelement when the movable element is deflected. The protrusion comprisesa conductive element electrically coupled to one of the interconnectlayers.

Some aspects of the present disclosure relate to a method of forming aMEMS device. The method includes forming an interconnect layer on afirst substrate and forming a dielectric layer over the interconnectlayer. A protrusion is formed on a top surface of the dielectric layer,the protrusion having a low surface energy relative the surface energyof the dielectric layer. The method further includes forming anelectrical path between the protrusion and a voltage potential node. Themethod yet further includes bonding a MEMS wafer to the dielectriclayer, and patterning the MEMS wafer to form a movable element. Theprotrusion is in a path of movement of the movable element when themovable element is deflected in a first direction.

Although embodiments of the present disclosure and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. For example, it will be readily understood by those skilled inthe art that many of the features, functions, processes, and materialsdescribed herein may be varied while remaining within the scope of thepresent disclosure. Moreover, the scope of the present application isnot intended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present disclosure,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present disclosure. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

1. A microelectromechanical system (MEMS) device comprising: asubstrate; a movable element at least partially suspended above thesubstrate and having at least one degree of freedom; and a protrusionextending from the substrate and configured to contact the movableelement when the movable element moves in the at least one degree offreedom, wherein the protrusion comprises a surface having a watercontact angle of higher than about 15° measured in air.
 2. The MEMSdevice of claim 1 further comprising an interconnect electricallycoupling the protrusion to a potential voltage node.
 3. The MEMS deviceof claim 2 wherein the potential voltage node is a ground node or apower supply voltage node.
 4. The MEMS device of claim 2 wherein thepotential voltage node is electrically coupled to the movable element.5. The MEMS device of claim 1 wherein the protrusion comprises siliconoxide and wherein the surface of the protrusion comprises a conductivefilm overlying the silicon oxide.
 6. The MEMS device of claim 5 whereinthe conductive film comprises a material selected from the groupconsisting essentially of TiN, AlCu, amorphous Carbon, a stacked film ofTiN/AlCu, and combinations thereof.
 7. The MEMS device of claim 1wherein the movable element is at least partially suspended above acavity in the substrate.
 8. The MEMS device of claim 1 furthercomprising a sense electrode positioned under the movable element andwherein the protrusion is positioned to contact the movable element whenthe movable element moves along the at least one degree of freedom priorto the sense electrode contacting the movable element when the movableelement moves along the at least on degree of freedom.
 9. The MEMSdevice of claim 1 wherein the protrusion comprises a conductor elementformed on the substrate.
 10. A MEMS device comprising: a first substrateand comprising a plurality of interconnect layers embedded in arespective plurality of stacked dielectric layers; a second substratemounted atop the first substrate and bonded to a topmost one of thedielectric layers, the second substrate comprising a movable element atleast partially suspended above the first substrate; and protrusionextending from the first substrate and configured so as to engage themovable element when the movable element is deflected, the protrusioncomprising a conductive element electrically coupled to one of theinterconnect layers.
 11. The MEMS device of claim 10 further comprisinga through silicon via (TSV) electrically coupling an element on thesecond substrate to an element on the first substrate.
 12. The MEMSdevice of claim 10 further comprising a sense electrode and wherein theprotrusion has a same height as the sense electrode, and further whereinthe protrusion is located such that the movable element when contact theprotrusion when the movable element is deflected and hence is preventedfrom contacting the sense electrode when deflected.
 13. The MEMS deviceof claim 10 further comprising a cavity in the first substrate andwherein the movable element is at least partially suspended above thecavity.
 14. The MEMS device of claim 13 wherein the protrusion islocated on a floor surface of the cavity.
 15. The MEMS device of claim10 wherein the protrusion comprises a silicon oxide protrusion coveredwith a conductive film.
 16. The MEMS device of claim 15 wherein theconductive film comprises a material selected from the group consistingessentially of TiN, AlCu, amorphous Carbon, a stacked film of TiN/AlCu,and combinations thereof.
 17. The MEMS device of claim 10 wherein theprotrusion comprises a metal feature formed on the first substrate. 18.A method of forming a MEMS device comprising: forming an interconnectlayer on a first substrate; forming a dielectric layer over theinterconnect layer; forming on a top surface of the dielectric layer aprotrusion having a low surface energy relative the surface energy ofthe dielectric layer; forming an electrical path between the protrusionand a voltage potential node; bonding a MEMS wafer to the dielectriclayer; and patterning the MEMS wafer to form a movable element, whereinthe protrusion is in a path of movement of the movable element when themovable element is deflected in a first direction.
 19. The method ofclaim 18 wherein forming on a top surface of the dielectric layer aprotrusion having a low surface energy comprises: patterning thedielectric layer to form a protrusion extending from a surface thereof;forming a conductive film over the patterned dielectric layer; andremoving the conductive film from at least a portion of the surface ofthe dielectric layer while leaving the conductive film overlying theprotrusion.
 20. The method of claim 18 wherein bonding the MEMS wafercomprises a silicon surface and the dielectric layer comprises a siliconoxide surface and bonding a MEMS wafer to the dielectric layer comprisesbringing the silicon surface and the silicon oxide surface into contact.21. The method of claim 18 further comprising electrically coupling theprotrusion to at one of a ground potential, a voltage potential, and apotential of the movable element during the manufacture of the MEMSdevice.
 22. The method of claim 18 wherein the step of forming on a topsurface of the dielectric layer a protrusion comprise forming a metalfeature on the top surface of the dielectric layer.